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1. A software module that extends or enhances the capabilities of an existing application
   - add-on
    
2. A printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities
   - circuit board, circuit card, board, card, add-in
    
3. An add-on piece of software that extends the features or functionality of a larger application

1. Plug into an outlet
   "Please plug in the toaster!";
   - plug into, connect

Derived forms: plugs in, plugged in, plug-ins, plugging in

Type of: computer software, enter, infix, insert, introduce, package, printed circuit, software, software package, software program, software system

Encyclopedia: Plug-in